This invention relates generally to electromagnetic circuit breakers of the type having a housing made in two half sections, each of which sections is molded from a plastic dielectric material. The half sections are held together by fasteners so as to support a circuit breaker mechanism and terminal components between these half sections.
Such circuit breakers are designed to provide load current and voltage through an electromagnetic coil that surrounds a delay tube in which a plunger or core is adapted to be drawn magnetically toward a pole piece at the end of the delay tube by the flux created in a frame and an armature. The frame is mounted between the circuit breaker half sections to support for both the coil, generally on a bobbin or the like, and also to support the circuit breaker mechanism that is adapted to be tripped by the movable armature.
The armature engages a sear to open the electrical contacts provided in an arc chamber that is also defined in the housing. The arc chamber may be vented to release gases generated when the contacts open. This avoids the build up of excessive heat and pressure within the circuit breaker housing.
prior art circuit breakers of this type often include angled slots which are generally molded into the half sections of the circuit breaker housing to receive U-shaped arc splitter plates that are arranged in spaced relationship along the path of movement for the movable contact as it travels from a closed position, in engagement with the fixed contact provided on one of the terminal studs in the circuit breaker housing, to an open position where it is spaced from the fixed contact. The movable contact is generally provided on the underside of the movable contact arm for this purpose. The contact arm provides for the electrical path through the movable contact to the fixed contact in the contacts closed condition of the circuit breaker.
The present invention relates to improving the arc suppressant capabilities of a circuit breaker. The improved circuit breaker of the present invention does not utilize arc splitter plates such as those used with prior art circuit breakers described above. In accordance with the present invention, a pair of magnets is provided supported by the housing on opposing sides of the path taken by the arc current. The arc current is generated between the movable and fixed contacts when the movable contact arm moves away from the fixed contact as the contacts open in response to an overcurrent.
The movable contact arm can be activated and moved away from the fixed contact generating an arc current, either by the circuit breaker mechanism in response to an overcurrent situation, or manually via a switch coupled to the circuit breaker mechanism. The arc current generates a magnetic field oriented concentrically of the axis or path of the arc current. The direction of the magnetic field is clockwise when viewed in the direction of the arc current, as can be determined by using the xe2x80x9cRight Hand Rulexe2x80x9d with respect to the direction of the arc current. This magnetic field generated by the arc current is referred to herein as a first magnetic field.
In accordance with the present invention, a second magnetic field is generated by a pair of magnets disposed on opposing sides of the arc current path. The magnets are arranged to generate the second magnetic field transverse to the first magnetic field. The first and second magnetic fields combine to deflect the arc current. The deflection of the arc current lengthens the path of the arc, which increases the voltage for the arc, thereby decreasing the current and providing less extreme conditions of heat and pressure inside the breaker housing as well as providing conditions for reliable arc extinction. The elongation of the arc increases the arc resistance and thereby increases the arc voltage. On direct current (D.C.) devices when the arc voltage is increased above the supply voltage the arc is extinguished rapidly. This is necessary on breakers where there is insufficient distance (gap) between the movable and stationary contacts.
The circuit breaker housing has a conventional vent opening near the deflected arc current so that heat and gas pressure generated by the arc current can escape, further reducing the heat and pressure interior the housing.
In further accordance with the present invention, the pair of magnets are preferably permanent magnets of the type containing neodymium. Alternatively, other types of magnets could be used without departing from the scope of the present invention.